Our visual system is specialized for central vision, which is served by the foveal region of the retina. High- acuity vision is possible only when the visual world is kept relatively stable on the retina. Visual image stability is preserved during head movements by the compensatory action of the vestibular ocular (VOR) and optokinetic reflexes (OKR). When an object of interest moves relative to the head, the VOR needs to be adjusted to maintain tracking. This adjustment is accomplished, in part, by the smooth pursuit (SP) system. Foveal SP is primarily a volitional behavior, which depends on processing of visual and eye movement information in cerebral cortex, brainstem and cerebellum. There are multiple pathways leaving frontal and parietal cortical areas, which contribute differentially to SP and visual-vestibular behavior. The long-term goal of our studies is to determine the specific SP-related information represented in parallel frontal- and parietal- brainstem pathways. Our proposed studies are designed to determine neural mechanisms responsible for converting visual motion information into commands for eye movements during different SP behaviors. Our overarching hypothesis is that the information processed in each parallel cortical-brainstem pathway differentially supports different aspects of SP including prediction, initiation, maintenance, gain control and adaptive modification. To test our hypothesis, projection neurons in FEF and MST cortex are identified using antidromic activation following delivery of electrical stimulation pulses in SP regions of the brainstem. We then use computational methods to compare and contrast the information carried in activated neurons located in layer-5 with non-activated neurons in other cortical layers. The significance of our work is that SP is compromised in different developmental or disease processes. Therefore, our studies are designed to test real SP circuits in a manner that will aid in the diagnosis and potential treatment of disorders associated with strabismus, neurodegenerative disease, brain injury and stroke. PUBLIC HEALTH RELEVANCE: We use eye and head movements to direct the line of sight so that objects of interest, whether stationary or moving, are imaged on the fovea of each eye. Damage to the cortical smooth pursuit system and distal circuits involving the brainstem and cerebellum results in loss of visual, vestibular and oculomotor function. Advancing our understanding of how signals are processed in parallel cortical-brainstem pathways could lead to improved diagnosis and treatment options for developmental disorders such as strabismus and acquired disorders associated with brain injury, neurodegenerative disease and stroke.